Short, small gage wire can carry some really large current draws, mainly because of the low resistance. A good example is the wires to the brushes in a large Router motor. There is high current draw there, but the brush wires are so short, there is very little resistance. The resistance is what causes a wire to heat up and burn out, or in our case heat up, increasing the resistance and lowering the voltage at the load end. The use of a larger gage wire on long runs reduces the overall resistance of the wire. The same is true in your house wiring. 14ga is standard for 15A outlets and lights, but when you reach a long run, somewhere around 80ft, the code calls for a larger gage wire, IE12 gage. There is alsoa limit on the drops, IEoutlets or switches , on a run because each of them add an amount of resistance. Servo leads are the same, The more extension plugs along the path, the more voltage drop at the servo. I'm not sure any of our stuff though requires 18ga wire.

Don